(1) Technical Field
The present invention relates to a food receptacle or package for electronic oven cooking and a method for cooking the food by using the same. More particularly, it relates to a food receptacle for electronic oven cooking which comprises at least one steam controlling opening for adjustably maintaining the an internal pressure in the receptacle within a particular range and a method for cooking the food by using the same.
(2) Background Information
At present, frozen foods are widely cooked by using electronic, or microwave, ovens. However, satisfactory results can not be obtained because the cooked food becomes harder due to excessive time of cooking or, in contrast with this, the food is insufficiently thawed by too short time of cooking, even if the electronic oven is set at a time and a temperature indicated on the commercial frozen food package.
These disadvantages in electronic oven cooking are considered to be induced by the following causes:
(1) Electronic ovens are largely different from one another in mechanism of electron radiation, in shape of an angular portion and in range thereof.
(2) The temperatures of chilled or cold foods vary from -25.degree. C. to +10.degree. C., according to whether the foods have been placed in a large-sized cold storage facility or a refrigerator car, a place where a freezing chamber is located, or a condition where the foods are permitted to stand before use. There is an extremely large difference between the dielectric constant of food moisture in the glacial (frozen) state and the dielectric constant of food moisture in the aqueous (liquid) state.
(3) Generally, the frozen foods are also different from one another in moisture content, in oil content and in the other constituents. Particularly, in the glacial state of the food moisture, greatly different electronic oven heating conditions are required.
In addition to the above three causes, the following two causes are cited.
(4) In conventional cooking, the results are little affected by a difference of 5 to 10 minutes in cooking time. In electronic oven cooking, however, the difference of 10 to 20 seconds in cooking time may result in cooked food which is still cold, hard and dry due to excess moisture release, etc.
(5) In conventional electronic oven cooking, the electronic oven must be set for the time indicated for the frozen food as a rough approximation of the cooking time. However it is difficult to cook the frozen food properly for the reasons described above.
The food holding table of the electronic oven can not be uniformly heated. The table includes portions which are increased in temperatures by the electronic oven heating, and portions which do not undergo the electronic oven heating and are therefore not appreciably increased in temperatures. Consequently, different times are required for cooking suitably, depending upon portions of the table where the food is placed. Further, the radiation heating parts are entirely different from one another in shape of the radiation surface and in range, according to types of the electronic ovens. the times for defrosting and cooking vary, according to the kinds of the frozen foods. Even for the same kind of foods, appropriate times for defrosting and cooking vary according to amounts of the components contained in the frozen foods, such as moisture and oil. These different conditions cause variations in the results. Accordingly, it has been impossible to expect cooking results which are always satisfactory.
Describing the present situation of the cooked and half-cooked (or partially-cooked) frozen foods, as the conventional frozen foods, there are typically mentioned meat, fishes and shellfishes coated with flour ready for frying, a hamburger steaks and meat balls ready for grilling, and the like. There are also included vegetables such as corn, onion, potato and the like, either sliced or not, raw or partially cooked. All these frozen foods are, however, thawed once and there after fried, grilled or steamed once again, and they can not be eaten directly by thawing and heating in the electronic oven.
In the case that the already cooked frozen food is thawed and heated in the electronic oven, if fried frozen food with flour coating is entirely thawed, the moisture in the flour coating is evaporated, because dish-like open vessels made of glass or ceramic materials are commonly used.
Consequently, the food becomes harder and has an entirely different texture. In addition, the oil comes up to the surface of the food and thereby the balance of taste is lost. When grilled frozen food is thawed and heated in the electronic oven, the oil melted out of the food similarly gathers of the surface of the food, resulting in stickiness of the surface. Further, the surface of the food becomes harder and crumbly to give a different texture by heating the food for a longer period of time, although the frozen food can be entirely thawed. Furthermore, the frozen food which was boiled and sliced can be heated in the electronic oven without hindrance, if the heating is carried out after the food has been thawed. If the food is heated in the form of a frozen block, the outer portion thereof will be scorched while the inner portion thereof remains frozen. The higher the moisture content in the food, in other word, the more frozen moisture portions are contained in the food, the more this trend is pronounced. These are due to a significant difference between the dielectric constants of frozen parts and aqueous parts. This difference in dielectric constant is caused by quick loss of the moisture in the outer portion of the food, when the food is heated in the electronic oven, that is to say, by lack of moisture evaporation balance between the outer portion and the inner portion of the food. This is responsible for deterioration of the food quality. Because of these drawbacks, the cooked frozen foods have been limited to extremely few kinds. Niku-mans (meat buns), an-mans (bean-jam buns), shao-mais and gyozas have been naturally defrosting or rendered into a chilled state in a refrigerator from the frozen state, and thereafter the electronic oven has been used only for heating them. The frozen foods have seldom been directly treated in the electronic oven. Usually the frozen shao-mais are heated in the electronic oven after placing the frozen shao-mais on a dish, adding a predetermined amount of water thereto and covering the shao-mais with a wrapping film. In this method, the capabilities of the electronic oven are not sufficiently utilized. At present, the electronic oven is utilized only for minor purposes such as heating of sake, milk, wet towels and the like or defrosting of frozen cuttlefishes and prawns. The electronic oven was originally provided for the purpose of cooking the already-cooked, namely fried or grilled, frozen food such as fried meat, fishes and shellfishes with flour coating and grilled hamburgers. There are currently not available, however, already-cooked frozen foods packed in receptacles ready for electronic oven heating. The frozen foods presently available at shops are packed in ordinary paper dishes or paper boxes. The foods available for electronic oven heating are sold in the refrigerated condition because the frozen foods have the drawbacks noted hereinbefore. Foods which have been transported frozen are thawed before heating in the electronic oven. This is not a procedure in which the foods are directly cooked from the frozen state, and therefore the original purpose of the electronic oven is not fulfilled.
Moreover, the heating of the foods in the electronic oven is usually carried out in containers made of glass or ceramic materials. In this case, oil and moisture released during heating of fried or grilled oil-containing foods, such as chicken nuggets and hamburgers, adhere to the finger when the foods are removed from the containers, or to the containers and the oven surfaces. This is messy, and the heating container and oven must be cleaned. To overcome these defects, paper or a paper container is usually used to absorb the oil and moisture. All of the problems, however, have not been completely solved.
Thus, the electronic oven can not be fully utilized for its intended purpose for the reasons described above. More particularly, accurate measures of the required cooking times of the electronic oven can not be known and a difference of 10 to 20 seconds in cooking time can drastically alter the texture and the taste of the resulting food. These are the main reasons that the electronic oven, which should be highly convenient, has not been utilized for cooking the various foods and the availability of pre-packed, frozen cooked foods has been limited.